Vehicle fuel consumption and vibration reductions are very desirable; the desirability of the former being due to governmental regulations regarding tailpipe emissions and corporate average fuel economy, as well as to concerns related to the rising cost of gasoline and the rather limited existing worldwide supply of oil, while the desirability of the latter is due to a desire to provide a rather "smooth" and comfortable ride for the drivers and/or occupants of the vehicle.
As an engine is "started", the engine block rotates upon its mounts and generates vibrations which are undesirably coupled to the passenger compartment. Moreover, as the engine is "stopped", it typically reverses direction and further causes undesirable engine mount vibrations which are undesirably coupled to the passenger compartment. Additionally, as the engine is "started" or "stopped", the engine assumes and/or produces characteristic vibrational frequencies which are substantially similar to the low frequency resonant modes of the vehicle drivetrain, thereby undesirably exciting the drivetrain and further producing undesirable vehicle vibrations which are communicated to the passenger compartment and which potentially and structurally damage the drive train.
Moreover, fuel is unnecessarily consumed each time that the vehicle is in an idle state (e.g., each time that the engine is operating but the vehicle is not moving, such as at a stop sign or at a red traffic light), since fuel is combusted without producing vehicle motion. Therefore, "start/stop" powertrains are being designed for automotive vehicles in which the engine is stopped during those times when the vehicle would normally be in an idle state, and started automatically upon a driver demand for vehicle motion, such as when the accelerator is depressed. This "start/stop" powertrain therefore enables an overall improvement in fuel efficiency of the vehicle. With the attendant increase in the number of engine "starts" and "stops", and in light of the fact that these engine "starts" and "stops" are not explicitly commanded by the vehicle operator, there is a need to reduce the amount of undesired vehicle vibrations caused during the starting and stopping of the engine. Applicant's invention addresses these needs.